Though commonly used for sport, most of the fish in the Valley’s canals were put there to work. Starting in 1989, Valley utility company Salt River Project began stocking the canals that crisscross greater Phoenix with sterilized white amur carp. Their fishy mission: Feast on weeds and other fast-growing vegetation that flourish in the canals and slow down the flow of water.

Dubbed the White Amur Fish Program, it replaces the machinery and herbicides once used to clear canal weeds; both techniques were expensive, and the latter was environmentally specious. According to SRP environmental scientist Brian Moorhead, the carp – which live five to nine years – save the water utility at least $300,000 a year. SRP increased the number of fish introduced into the canal gradually through 2005; currently, 35,000 to 38,000 of the hearty, torpedo-shaped bottom-feeders feast on Valley weeds. Annual stocking in the spring keeps that figure constant.Though the amur program saves money, it required a lot of planning and energy to fine-tune. Besides fish-procurement and environmental-testing costs, a network of grates needed to be built within the canal system to allow SRP to control the number of fish in any given section. This is important both for amur safety – every winter, SRP drains sections of the canal for maintenance, and must herd the carp to safe areas – and the safety of native ecosystems. Amur are indigenous to China and were chosen for their ability to eat like sumo wrestlers, and because they can tolerate a wide temperature range.

SRP’s amur are imported from fish farms in Arkansas, fully sterilized. Otherwise, they would reproduce uncontrolled, and their progeny could make their way into natural water sources and wreak havoc. The sterilization process is complicated, but the upshot is that fish-farm workers collect eggs and sperm from normal adults, mix it in a steel cylinder, and pressurize it. This creates a third set of sex chromosomes that prevents reproduction. “It’s been a very good way of controlling their population,” Moorhead says.

Amur occupy almost all of SRP’s canal sections. It takes 35 to 50 fish per surface acre to adequately clear the weeds, and some sections swarm with more vegetation than others, so the number of amur varies per section.

Interestingly, SRP’s carp program helped spawn another singular breed: the urban angler. Many fish-eaters avoid the bony carp; however, Hemphill says it tastes “great” as long as you cut the brown part of the meat away. “Most people think they can’t be good because they’re algae eaters, but it’s all in how you prepare it and season it,” he says.

Though SRP prefers that people fish elsewhere, anglers are permitted to cast in the canals given the proper state fishing license, Moorhead says. However, white amurs must be released back into the water if caught. And even then, SRP will lose some fish; many will instinctively swallow the hook and die.

“And then we lose an employee, basically,” Moorhead says. “If they’re not doing their job, then we either have to replace them, or deal with more weed growth.”

• SRP is one of Arizona’s largest water suppliers. The utility company delivers about 325,851 gallons of water to metro Phoenix every year through its 131-mile canal system.

• Phoenix has 181 miles of canals, more than Venice (125 miles) and Amsterdam (47 miles) combined.

• The SRP canals run throughout the Valley, from 99th Avenue in the west to Power Road in the east, and from Greenway Road in the north to around Ocotillo Road in south Chandler.

• A seven-pound amur fish can eat three-quarters of its weight in weeds every day.

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